Power diode elements connected in reverse parallel to switching elements such as IGBT and MOSFET, may cause breakdown depending on used conditions if a time rate of current change (di/dt) is excessive at the time of recovery transition from a forward state to a reverse state. Such power diode elements are therefore typically required to have a large di/dt value in the event of breakdown, namely, to have high destruction immunity during reverse-recovery (hereinafter called “reverse-recovery immunity”).
JP2014-003271A discloses that an extraction region having a greater depth than an anode region is formed on the outer side of and in contact with the anode region, so as to relax electric field crowding on an outer curvature portion (outer curved portion) of the extraction region to ensure improved reverse-recovery immunity.
The required reverse recovery value di/dt with regard to the reverse-recovery immunity tends to increase year by year. Such an increase leads to an anxiety about breakdown due to current crowding on an outer edge where the anode electrode is connected to the anode region, or breakdown due to electric field crowding on the outer curvature portion of the extraction region. Thus, there remains a need for further improvement of the reverse-recovery immunity.